1. Field of the Invention
The present invention relates to an electron emitting device extensively applicable to such apparatus as high-frequency amplifiers, microwave oscillators, light emitting devices, and electron beam lithography apparatus.
2. Related Background Art
The conventional electron emitting devices (electron sources) having been used heretofore include thermionic emission sources using a tungsten filament, cold cathodes using lanthanum hexaboride, thermal-field emission cathodes using zirconia-coated tungsten, and so on. Among materials applied to these electron emitting devices, diamond is drawing attention in recent years because of possession of negative electron affinity. Examples of the known electron emitting devices of this type include the electron emitting device in which a metal cathode is coated with diamond, as described in Journal of Vacuum Science and Technology B 14 (1996) 2060 (Document 1), the electron emitting device in which a layer with continuously varying bandgap is formed in a diamond emitter of projecting shape, as described in Japanese Patent Application Laid-Open No. 11-154455 (Document 2), in order to effectively utilize the negative electron affinity of diamond, and the electron emitting device using a pn junction of diamond, as described in Japanese Patent Application Laid-Open No. 4-67528 (Document 3).